Motorola MC144144P Datasheet
SEMICONDUCTOR TECHNICAL DATA
Advance Information
CMOS
The MC144144 is a Line 21 closed–caption decoder for use in television
receivers or set–top decoders conforming to the NTSC standard. Capability for
processing and displaying all of the latest standard Line 21 closed–caption
format transmissions is included. The device requires a closed–caption
encoded composite video signal, a horizontal sync signal, and an external
keyer to produce captioned video. RGB and box signal outputs are provided,
which along with the mode select, allow simple interfacing to either color or
black–and–white TV receivers.
Display storage is accomplished with an on–chip RAM. A modified ASCII
character set, which includes several non–English characters, is decoded by an
on–chip ROM. An on–screen character appears as a white or colored dot matrix
on a black background.
Captions (video–related information) can be up to four rows appearing
anywhere on the screen and can be displayed in two modes: roll–up, paint–on,
or pop–on. With rollup captions, the row scrolls up and new information appears
at the bottom row each time a carriage return is received. Pop–on captions work
with two memories. One memory is displayed while the other is used to
accumulate new data. A special command causes the information to be
exchanged in the two memories, thus causing the entire caption to appear at
once.
When text (non–video related information) is displayed, the rows contain a
maximum of 32 characters over a black box which overwrites the screen.
Fifteen rows of characters are displayed in the text mode.
An on–chip processor controls the manipulation of data for storage and
display . Also controlled are the loading, addressing, and clearing of the display
RAM. The processor transfers the data received to the RAM during scan lines
21 through 42. The operation of the display RAM, character ROM, and output
logic circuits are controlled during scan lines 43 through 237. The functions of
the MC144144 are controlled via a serial port which may be configured to be
either I2C or SPI.
• Conforms to FCC Report and Order as Amended by the Petition for
Reconsideration on Gen. Doc. 91–1
• Conforms to EIA–608 for XDS Data Structure
• Supports Four Different Data Channels for Field 1 and Five Different Data
Channels for Field 2, Time Multiplexed within the Line 21 Data Stream:
Captions Utilizing Languages 1 and 2, Text Utilizing Languages 1 and 2
and XDS Support
• Output Logic Provides Hardware Underline Control and Italics Slant Generation
• Single Supply , Operating Voltage Range: 4.75 to 5.25 V
• Supply Current: 20 mA (Preliminary)
• Operating Temperature Range: 0 to 70°C
• Composite Video Input Range: 0.7 to 1.4 V p–p
• Horizontal Input Polarity: Either Positive or Negative
• Internal Timing and Sync Signals Derived from On–Chip VCO
Order this document
18
1
ORDERING INFORMATION
MC144144P Plastic DIP
PIN ASSIGNMENT
V
1
SS
GREEN
VIDEO
CSYNC
2
BLUE
3
SEN SCK
4
HIN
5
SMS
6
7
8
LPF
9
P SUFFIX
PLASTIC DIP
CASE 707
18
17
16
15
13
12
11
10
by MC144144/D
RED
BOX
SDO
SDA14
VIN/INTRO
V
DD
VSS(A)
RREF
In this document, the term ‘user’ refers to the television or VCR designer. The user may choose to make certain optional features selectable by
the viewer. These features then become viewer options.
This document contains information on a new product. Specifications and information herein are subject to change without notice.
REV 1
11/95
Motorola, Inc. 1995
MOTOROLA
MC144144
1
ROW
ADDR BUS
COMMAND
PROCESSOR
BLOCK DIAGRAM
MUX
ADDRESS
10
DISPLAY
RAM
DEC
ADDR
GEN
CHARACTER
13
ADDR
DECODER
OUTPUT
LOGIC
RED
GREEN
BLUE
BOX
17 3 2 18
+ 5 V
6 4 15 14 16
13
VDO
12
SDO
SDA
SCK
SEN
SMS
INTRO
VIN/
DATALINE
SLICED
PORT
SERIAL
CONTROL
DATA BUS
DATA CLK
RECOVERY
DATA
DATA
SLICER
BUFFER
STATUS REG
AW FEW
LOCK
SIG
TEST REG
VW
DIG
II LOCK
PG
4
ROW
SYNC
SLICER
LATCH
6
DOT CLK
DIV
DOT CLK
COMP SYNC
CHAR CLK
V LOCK
8
LATACH
DISPLAY
CHAR
CW
FLD
CIR
MSGR
4
OSCO/S
SS CTR
FLD
CTR
LINE & FLD
LS
????
SFLP
CONTROL
& MUX
I DRIVE
V/I
CKT
POR
REF
LINE AND FLO
10
RREF
(A)
SS
V
DECODERS
111
SS
V
9
LPF
LOOP
FILTER
MC144144
2
7
VIDEO
DUAL
CLAMP
SLICE LEVEL
8
CSYNC
CG LINES
CG
LOGIC
MSYNC
PH1
PH2
FR
5
HIN
MOTOROLA
ABSOLUTE MAXIMUM RATINGS* (Voltages referenced to V
Á
Á
Á
Á
Symbol
VDD(A)
VDD(D)
V
in
V
out
I
in
I
out
I
DD
P
D
T
stg
T
L
ÁÁ
Analog DC Supply Voltage
Digital DC Supply Voltage
DC Input Voltage Analog Section
DC Output Voltage, Digital Section
DC Input Current, per Pin
DC Output Current, per Pin
DC Supply Current
Power Dissipation, per Package
Storage Temperature
Lead Temperature, 1 mm from Case for
10 Seconds
БББББББББ
Parameter
Digital Section
– 0.5 to 6.0
– 0.5 to 6.0
– 0.5 to VDD(A) + 0.5
– 0.5 to VDD(D) + 0.5
– 0.5 to VDD(D) + 0.5
– 65 to + 150
БББББ
SS(A)
Value
+ 10
+ 20
+ 30
300
260
and V
SS(D)
Unit
mA
mA
mA
mW
°C
°C
)
V
V
V
V
Á
This device contains protection circuitry to
guard against damage due to high static voltages or electric fields. However, precautions
must be taken to avoid applications of any voltage higher than maximum rated voltages to
this high–impedance circuit.
* Maximum ratings are those values beyond which damage to the device may occur.
Functional operation should be restricted to the limits in the Electrical Characteristics
tables or Pin Description section.
DC ELECTRICAL CHARACTERISTICS
(VDD(A) = VDD(D) = 4.75 to 5.25 V, TA = 0 to 70°C, Voltages Referenced to VSS(D) Unless Otherwise Indicated)
Symbol
V
IL
V
IH
V
OL
V
OH
I
IL
I
CC
Kφ
I
LP
Input Voltage Low
Input Voltage High
Output Voltage Low
Output Voltage High
Input Leakage
Supply Current
VCO Gain
Loop Filter Current
*The estimated value is 20 mA; this is not guaranteed.
Parameter
Conditions
IOL = 1.0 mA
IOH = 0.75 mA
0 V, V
CC
Estimated
Min
0
0.7 V
CC
—
VCC – 0.4
– 3.0
—
—
—
Max
0.2 V
V
0.4
3.0
TBD
TBD
CC
—
20
CC
Unit
V
V
V
V
µA
mA
MHz/V
mA
MOTOROLA
MC144144
3
AC AND TIMING CHARACTERISTICS
Parameter Conditions
Composite Video Input
Amplitude: 1.0 Vp–p, ± 3 dB
Polarity: Sync tips negative
Bandwidth: 600 kHz
Signal Type: Interlaced
Max Input R: 470 Ω
DC Offset: Signal to be ac coupled with a minimum series capacitance of 0.1 µF.
Non–Standard Video Signals Must Have the Following Characteristics
Sync Amplitude: 200 mV min
Vert Pulse Width: 3H ± 0.5H
Vert Pulse Tilt: 20 mV max
H Timing: Phase Step (head switch) ± 10 µs max
Horizontal Signal Input (Preferably H Flyback)
Amplitude: CMOS level signal, low ≤ 0.2 VCC, high ≥ 0.7 V
Video Lock Mode:
Polarity:
Frequency:
HIN Lock Mode:
Polarity:
Frequency:
Line 21 Input Parameters ( at 1.0 Vp–p)
(Line 21 must be in its proper position to the leading edge of the vertical sync signal.)
Code Amplitude: 50 IRE ± 10 IRE
Code Zero Level: – 5 IRE, + 15 IRE relative to back porch
Bit Rate: 32 x F
Start of Code: 10.5 ± 1.0 µs
Start of Data: 3.972 µs, – 0.00 µs, + 0.30 µs
Input Signal–to–Random Noise Performance
Unit will function down to a 25 dB ratio
(CCIR weighted
Internal Sync Circuits
The internal sync circuits will lock to
all 525 line or 625 line signals having
a vertical sync pulse.
Timing Signals
Dot Clock: 768 x FH = 12.0839 MHz
Dot Period: 82.75 ns
Character Cell Width: 1.324 µs (tH ÷ 48)
Width of Row (Box): 45.018 µs (34 chars = 17/24 x tH)
Width of Row (Char): 42.370 µs (32 chars = 2/3 x tH)
Fh Deviation (long term) ± 0.5% max
Fh p–p Deviation (short term) ± 0.3% max
CC
Any
15,734.263 Hz, ± 3%
Any
Display HFB pulse
h
(Measured from the midpoint of the leading edge of video H pulse to the midpoint
of the rising edge of the first clock run–in cycle.)
(Measured from the midpoint of the falling edge of the last clock run–in cycle to the
midpoint of the rising edge of the start bit.)
One error per row or better at that level.
It is at least 2 H long.
It starts at the proper 2 H boundary for its field.
If equalizing pulse serrations are present they must be less than 0.125 H in width.
MC144144
4
MOTOROLA
AC AND TIMING CHARACTERISTICS (continued)
Parameter Conditions
Horizontal Timing
The timing of the ouput signals box
and RGB have been set to make a
centered display.
Control Port Signals – Two–Wire Serial Mode (SMS = LOW, SEN = HIGH) (See Figure 10)
Clock and Data Transitions: The SCK
and SDA bus lines are normally pulled
high with a resistor. Data on the SDA
bus may only change during SCK low
time periods. Data changes during
SCK high periods will indicate a start
or stop condition.
Acknowledge: All address and data
words are serially transmitted to and
from the MC144144 in eight bit words.
A ninth bit time is used for the
acknowledge.
Control Port Signals – Three–Wire Serial Mode (SMS = HIGH) (See Figure 11)
Three–wire bus with Clock signal on
SCK pin, Serial Data Input on SDA
pin and Serial Data Output on SDO
pin.
The positioning of these outputs can be adjusted in 330 ns increments by writing a
new value to the H Position Register.
Start Condition: A high–to–low transition of SDA with SCK high is a start condition
which must precede any other command.
Stop Condition: A low–to–high transition of SDA with SCK high is a stop condition
which terminates all communications.
The acknowledging device does so by pulling the SDA bus low during the ninth
bit.
SEN pin LOW disabled the port, placing SDO in three–state. Signal transitions on
SCK and SDA are ignored.
SEN pin HIGH enables the port for operation.
SEN and SMS pins LOW is a hardware reset for the part. These pins must be held
low for at least 100 ns.
Serial synchronization can be established by clocking in the minimum required
SSR string of FFh, FFh, FEh. More than two bytes of FFh may be input but the
string must end with FEh.
MOTOROLA
MC144144
5
(REFERENCE WHITE)
100 IRE
0 IRE
(BLANKING LEVEL)
COLOR
BURST
CHAR 1
CHAR 2
CHAR 3
CELL WIDTH = 1.324
µ
s
CHAR 32
–40 IRE
13.5 µs
35.73 µs
CENTER OF ACTIVE VIDEO
COMPOSITE
VIDEO
NOTES:
1. Timing parameters derived from the
2. Dot period = 82.76 ns.
3. An assumption is made that the delay through the low–pass filter is 220 ns. Therefore, the timing of the output signals is normally set so
that the start of the leading box preceding the first displayable character cell occurs at 13.4 to 13.7 µs after the midpoint of the leading edge
of the horizontal sync pulse at Point A. The 13.4 to 13.7 µs value may be altered via a mask option; contact your Motorola representative.
A
LOW–PASS
FILTER
NAB Engineering Handbook
VIDEO
IN
, 7th Edition, page 5.4–75.
CHAR LUM = 42.370 µs
BOX = 45.018 µs
MC144144
OUTPUTS
Figure 1. Timing of Output Signals Relative to Composite Video at Point A
MC144144
6
MOTOROLA
INTRODUCTION
THE MC144144 DECODER
The MC144144 is a stand alone integrated circuit, capable
of processing VBI data from both fields of the video when the
data conforms to the transmission format defined in the Television Decoder Circuits Act of 1990 and in accordance with
the EIA–608.
The Line 21 data stream can consist of data from several
data channels multiplexed together. Field 1 has four data
channels, two Captions and two Text. Field 2 has five additional data channels, two Captions, two Text, and Extended
Data Services (XDS). The XDS data structure is defined in
EIA–608.
In this document, the term “user” refers to the television or
VCR designer. The user may choose to make certain optional features selectable by the viewer. These features then become viewer options.
DATA TRANSMISSION FORMAT
The composite data signal contained within the active portion of the VBI line consists of a seven–cycle sine–wave
clock run–in burst, a start bit, and 16 bits of data. These 16
bits consist of two 7–bit characters and control codes, with
odd parity, that conform to the FCC closed caption decoder
requirements and EIA–608. The clock rate is 0.5035 MHz
which is 32 x FH. The clock burst and data packet are 50 IRE
units peak–to–peak and are filtered to a “2T” response. Data
is sent with the least significant bit (bit b0) being sent first and
the most significant bit (bit b7, the parity bit) being sent last.
MC144144 FEA TURE SUMMARY
The primary features of the MC144144 are briefly described below.
VBI Data Processing
The MC144144 extracts the data in Line 21 of the incoming video. All data channels in both fields are handled. Specifically, the MC144144 can:
• Process data from both fields of Line 21 simultaneously .
• Display data from any data channel.
• Output XDS data through the serial port while displaying
selected data.
• Output XDS data raw or filtered.
• XDS filter parameters user selectable from a list of pre–pro-
grammed values.
• NTSC or PAL operation selectable.
Video Data Display Modes
The data extracted from the incoming video may be displayed in different ways, according to the user selection and
the type of data. The display features available are:
• Ten different data display modes, CC1–CC4, T1–T4, and
two XDS displays.
• Pop–on, Paint–on, and Roll–up CAPTION displays.
• TEXT display default is a full–screen, 15–row display .
• User able to vertically reduce and reposition the TEXT dis-
play as desired.
• Color or Monochrome display mode selectable.
• XDSG Display Mode (channel grazing):
Network Name, Call Letters,
Program Name,
Program Length, Time In Show
• XDSF Display Mode (full information):
XDSG Display Mode information plus:
Program Type (only basic types),
Program Description.
Control Port Data Display Modes
In addition to displaying data extracted from Line 21 of the
incoming video, the MC144144 can display information supplied through its serial port. This is referred to as the on–
screen display (OSD) mode. This mode provides:
• OSD display can use all Video Data Display modes and
features.
• Additional graphics features available.
• Double high and double wide characters available.
• Information may be placed anywhere on the screen.
• OSD display can be locked to an external V signal, if
desired, to provide an OSD display when no video is
present.
Character Set
The MC144144 has a new character set with extended
features. For example:
• New font with lowercase letters having descenders.
• Optional display mode using drop shadow.
• EIA–608 extended characters.
• EIA–608 background and foreground attributes.
• Special framing and graphics for OSD display .
• Double high and double wide character display for OSD.
• Fifteen scan lines per character row for OSD and TEXT.
Serial Communications Interface
Communications and control of the MC144144 are
through a serial control interface. Two serial control modes
are available with the MC144144 performing as a slave device. These modes are:
• A two–wire, I2C interface.
• A three–wire, serial peripheral interface (SPI).
Five pins are dedicated to the control port function and one
pin can be configured to provide an interrupt output. These
pins are designated as:
SMS = Serial mode select.
SCK = Serial port clock for either serial mode.
SDA = Serial port data for I2C mode and data In for
SPI mode.
SDO = Serial data out for SPI mode. Not used in I2C
mode.
SEN = SPI mode enable signal. Must be HIGH for I2C
mode.
VIN/INTRO = INTRO mode = Interrupt output on
selected event (when used).
I2C Mode
• I2C mode is selected by bringing the SMS pin LOW and
SEN pin HIGH.
• Acts as a slave device.
• SDA and SCK pins are the data and clock lines of this port.
MOTOROLA
MC144144
7
• When used, INTRO can be enabled to interrupt on selected
events.
• When SEN pin is made LOW the part will be reset.
SPI Mode
• SPI mode is selected by making the SMS pin HIGH.
• Acts as a slave device.
• All communications are clocked in and out as 8–bit bytes.
• SCK is the serial clock (input), SDA is Data In, and SDO is
data out.
• SEN pin enables communication. When it is LOW the SDO
pin is three–state.
• When SEN is brought HIGH the part will be synchronized
and waiting for a command.
• If SEN is tied HIGH, the part can be synchronized by a
command string.
• When used, INTRO can be enabled to interrupt on selected
events.
• When SEN and SMS pins are made LOW the part will be
reset.
Setup and Operational Control
User Selectable Displays are:
Captions, Language I, Field 1 (CC1)
Captions, Language II, Field 1 (CC2)
Captions, Language I, Field 2 (CC3)
Captions, Language II, Field 2 (CC4)
Text, Language I, Field 1 (T1)
Text, Language II, Field 1 (T2)
Text, Language I, Field 2 (T3)
Text, Language II, Field 2 (T4)
XDSG Display Mode
XDSF Display Mode
OSD mode (through the serial port)
User Controlled Features are:
Decoder ON/OFF
Color or Monochrome Output
EIA–608 Extended Attributes ON/OFF
OSD Drop Shadow ON/OFF
Text box size, Number of rows = x
Text box position, Base row = y
TV lines per character row, 13 or 15
Erase Timer (16 s) ON/OFF
Data Output Modes (through the serial port)
XDS Data Output, Raw or Filtered
Selected Channel and XDS Activity Indicators
Video Lock Indicator
Setup Options:
Horizontal timing of BOX
NTSC or PAL H lock source, Video or EXT HIN
V lock source, Video or EXT VIN
Default Condition Following Reset
Display Channel = CC1
Decoder = OFF
TEXT Size = 15 Rows
Lines/Row = 13
Background = BOX
Extended Attrib = ON
Data Outputs = OFF
NTSC operation
VCO Lock = Video
BOX Timing = 13.5 µs
Vert Lock = Video
VIN/INTRO = INTRO and Disabled
Horiz Lock = Video
Color/Mono = Color
OSD Display = Drop Shadow
OSD Display = 15 Lines/Row
OVERVIEW OF THE LINE 21
CLOSED CAPTION SYSTEM
THE LINE 21 CLOSED–CAPTIONING SYSTEM
The Line 21 closed–captioning system provides for the
transmission of caption information and other text material as
an encoded composite data signal during the unblanked portion of Line 21, field 1 of the standard NTSC video signal. In
addition, a framing code is transmitted during the first half of
Line 21, field 2.
The encoded composite video signal for Line 21, fields 1
and 2 is shown in Figure 5. The video signal conforms to the
standard synchronizing waveform for color transmission given in Sub–part E, Part 73 of the FCC Rules and Regulations.
Multiplexed Data Channels
The Line 21, field 1 closed–caption system defines four different data channels which can be time multiplexed within
the Line 21 data stream. They are Captions — Language 1,
Captions — Language 2, Text — Language 1, and Text —
Language 2. Both languages may be English in either case.
Field 2 has five additional data channels, two Captions,
two Text, and Extended Data Services (XDS). The XDS data
structure is defined in EIA–608.
DATA FORMAT
The composite data signal contained within the active portion of the VBI line consists of a seven–cycle sine–wave
clock run–in burst, a start bit, and 16 bits of data. These 16
bits consist of two 8–bit alphanumeric characters formulated
according to the USA Standard Code for Information Interchange (USASCII;x3.4–1967) with odd parity . The clock rate
is 0.5035 MHz which is 32 x FH. The clock burst and data
packet are 50 IRE units peak–to–peak and are filtered to a
“2T” response. Data is sent with the least significant bit (bit
b0) being sent first and the most significant bit (bit b7, the
parity bit) being sent last.
MC144144
8
MOTOROLA
The data channels for each field are transmitted in Line 21
of that field as a time multiplexed data stream. The start of a
particular channel’s data stream is identified by the occurrence of one of its unique command codes. Once a unique
command code is received, all subsequent data is considered to belong to that data channel until a unique command
code is received for another data channel.
The 7–bit ASCII table defines two types of information:
printing and non–printing. Printable data are data bytes having values between x0100000 ($20) and x1111111 ( $7 F) ,
where x represents the parity bit. Data bytes having values
between x0000000 ($00) and x0011111 ( $1 F) a re called
non–printing characters, because they have no displayable
character font in the standard ASCII table.
10.50 ±0.5 µs
10.076 µs
12.910
µ
s
4.15
±
0.1 µs 33.764 µs
1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526
Figure 2. Encoded Composite Video Signal
Displayable Character Set
The specifications define a modified ASCII table character
set where eight of the alphanumeric characters have been
changed to provide some non–English characters. Also, 15
additional characters are defined by special character commands. The changes in the ASCII table characters are
shown in Table 1.
T able 1. Modifications to the ASCII Characters
Hex
Code
2A * a′
5C \ e′
5E ^ i′
5F o′
60 ’ u′
7B { c
7D } N
7E
ASCII
Character
~
Line-21
Character
ç
~
~
n
Fifteen additional displayable characters are sent by transmitting a two–byte code. The sixteenth code provides a
transparent space. The byte pair has a non–printing character followed by a printing character, where the non–printing
character is $11 for Language 1 and $19 for Language 2. The
printing character determines the special character font that
is displayed according to Table 2.
Commands and Special Information
Data channel commands and special information are
transmitted as two–byte pairs consisting of a non–printing
0.12
µ
s
P
b1
b3 b5 b7 b1
b2 b4 b6
CHARACTER 1 CHARACTER 2
A
b2 b4 b6
R
I
T
Y
b3 b5 b7
P
A
R
I
T
Y
2.0
µ
s
character followed by a printing character. The two bytes of
the pair must be transmitted in the same field, and the pair is
transmitted twice in successive frames. This redundancy
provides some immunity to noise errors for control information.
Throughout the Line 21 system, bit 4 of the non–printing
character identifies the language. Bit b4 = 0 signifies Language 1 commands and b4 = 1 signifies Language 2. The
non–printing characters used in the Line 21 system are $10
through $17 for Language 1 and $18 through $1F for Language 2.
T able 2. Additions to the ASCII Characters
Print Character
30
31 °
32 1/2
33
34
35 ¢
36
37 “1/8 note” music symbol
38 a
39 “Transparent Space”
3A e
3B a
3C e
3D
3E o
3F u
¿
o
′′
^
^
^
l
^
^
MOTOROLA
MC144144
9
OPERA TING CHARACTERISTICS
DECODER OPERATION
The MC144144 provides full function NTSC, Line 21 performance. Input commands are included to enable the decoder to process and display any of the eight caption/text
data channels (CC1, CC2, CC3, CC4, T1, T2, T3, or T4) contained in Line 21 of either field of the incoming video. XDS
displays can also be selected. ON/OFF commands control
the screen displays. When switched to the decoder off (TV)
state, incoming data in the selected channel will still be processed but not displayed.
The MC144144 can also be configured to operate with
P AL video signals. It will decode information encoded into its
VBI in Line 22. The encoded data must conform to the waveform and command structure defined for NTSC, Line 21 operation.
DECODER SET–UP
VCO Lock
The design includes a VCO with stable gain characteristics
and good power supply rejection. The internal horizontal and
vertical synchronizing circuits provide a high degree of noise
immunity. There are options for both horizontal and vertical
lock. The VCO can be phase locked either to the horizontal
signal derived from the video input signal (VIDEO) or to the
externally supplied HIN signal, typically horizontal flyback.
HIN lock is used to provide a display having a minimum of
observable jitter. This requires an HIN signal derived from
the TV display and of the proper polarity. Such a signal is
readily available in a television receiver. VIDEO lock mode
enables the VCO to lock in phase to the incoming video
signal, thus providing good operation in an application where
no display related HIN signal is available, such as in a VCR.
Timing
Timing signals are derived from the VCO for use in the line
counting and display circuits. Line counting requires proper
identification of the input signal’s vertical pulse. Default operation uses the vertical sync signal derived from the video
input signal as the source for vertical lock. This method results in locking characteristics having good performance and
good noise immunity.
In the event that OSD operation is required under conditions when no input video is present, it would be necessary to
set the MC144144 for VIN lock. In this mode, the vertical timing will be determined from the vertical pulse signal supplied
to the VIN pin.
The horizontal position of the caption display is determined
by the internal timing circuits. A default condition has been
established that should result in a well centered display in a
typical application. However, since signal delays through
video processing circuits can vary between designs, the
MC144144 provides the user with the ability to change the
default timing. No matter which of the horizontal lock modes
is selected, the display horizontal position on the screen can
be adjusted in quarter character (330 ns) steps by serial port
commands.
DISPLAY FORMATS
Normal Mode
Characters are displayed as white or colored, dot–matrix
characters on an opaque background. The box is normally
black but the MC144144 can be set to blue by a serial command. The characters are described by a 12–by–18 dot pattern within a character cell which is 16 dots wide by 26 dots
high per frame. The location of the character luminance within the character cell varies from character to character to allow for the display of lower case letters with descenders. All
characters have at least a one dot border of black around
each character. Underline is also provided.
The character ROM consists of a 12–by–18 dot–matrix
pattern per character. Figure 3 shows the character font. Alternate rows and columns are read out of each field to produce an interleaved and rounded character. A display row
contains a maximum of 32 characters plus a leading and
trailing blank box, each a character cell in width, making the
overall width of a display row 34 x 8 = 272 dots. Successive
display rows are butted together, so that the total display is
195 dots high.
The black box (34 character cells wide by 195 dots high)
results in a box size of 45.018 µs in width by 195 scan lines in
height. Box starts in scan line 43 and extends to scan line
237. Theoretically , the display will be horizontally centered in
the video display when box starts 13.2 µs after the leading
edge of H. The default setting of the MC144144 places the
center of the box at about 13.5 µs to allow for some delay in
the normal video path. However, the box horizontal position
can be adjusted by the user in 330 ns increments. The display will be approximately within the safe title area for NTSC
receivers. Character width is 42.37 µs, also centered on the
screen, resulting in a leading and trailing 1.32 µs black border.
An optional caption display mode, drop shadow, can be
selected by the user through the serial port. This display
mode eliminates the black box around the characters and
places a two–dot black shadow to the right and below the
character luminance dots when in the 15 scan line per row
mode. This display mode is usable in captions, text, and
OSD displays. Figure 4 shows the characters with shadowing added.
Extended Features
EIA–608 defined new extended features such as optional
background and foreground display attributes and optional
extended characters. The MC144144 will always respond to
the extended characters but the extended background/foreground response can be controlled by the user. The background and foreground attributes add codes for background
colors, black foreground as well as transparent, opaque, and
semi–transparent background. The BOX signal output pin
will be set into a three–state condition whenever one of the
semi–transparent attribute codes is active. The external keying circuits can then use this condition to implement the intended video display.
The font for the extended characters is shown in Figure 5.
The accented capital letters have been implemented by placing the accent marks above the character cell. When
selected, this mode will result in the accent marks being written into the character cell space of the row above. In some
operating modes we will expand the size of the overall box
height by adding two additional scan lines at the top and one
additional line at the bottom. This will make room for the accent marks in the topmost row and add a black line below the
descenders of any lowercase characters in the last row.
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Figure 3. Display Character Font
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Figure 4. Display Character Font with Shadowing Added
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Figure 5. Display Character Font Extended Characters
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This approach was used because shrinking the capitals to
make room for the accent mark within the character cell
makes poor quality characters and in some cases there
would be no differentiation between the capital and lower
case letter. It also has the advantage of minimizing the ROM
size and providing a good readable font that closely matches
what is normally seen in print.
In the unlikely case of a conflict between an accented capital letter in one row and a lowercase descender in the same
character position in the row above, the descender is given
priority. It is believed that the improved readability of our approach over shrunk capital letters far outweighs this potential
conflict and results in a cost effective compromise for providing a full, extended features implementation.
The extended characters share their address space with
the ODS graphics characters. When a BOX display is used
the extended character set is in force. However, if a drop
shadow display is used the graphics characters are in force.
For caption and text display modes, if drop shadow is set, the
user must also command the MC144144 to switch back to
extended characters.
T ext Mode Display
When TEXT mode is selected normally , a black box will be
displayed as long as valid Line 21 code in the field selected is
being detected. The MC144144 provides the option to make
the box blue instead of black. This option will hold for captions as well as text.
The default TEXT display mode uses a 15 row by 34 character black box. TEXT characters will be displayed as they
are received starting in the top row. Successive carriage returns will move the display down successive rows until all 15
rows have been displayed. Thereafter, the text will scroll up
as new characters are added to the bottom row.
If the data for the selected channel is interrupted by a command for another channel, data processing stops but the display will remain. When a
data processing will resume and the new characters will be
added starting at the position that the display row/column
pointer was in at the interruption of data processing. If a
command is received, the display will be cleared and
text
new characters will be displayed starting in row 1, column 1
(left side).
The number of display rows and the location (base row) of
the TEXT box can be altered by the user. In this way, the user
can decide how much of the screen can be covered when
displaying non–program related information.
When scrolling, the display will shift one scan line per
frame until a complete row has been scrolled. If a carriage
return is received before scrolling is complete, the display will
immediately complete the “scroll” by jumping up the remaining scan lines and starts displaying the new text.
Caption Mode Display
According to the FCC specifications, caption data can appear in any of the 15 display rows but a single caption may
consist of no more than four rows. The form of the caption
display depends on the caption mode indicated by the transmitted caption command, pop–on, paint–on, or roll–up. The
MC144144 can display a single caption having as many as
eight rows. When any of the CAPTION display modes have
resume text command is received,
start
been selected, the screen will be transparent (display box is
only present when a caption is being displayed).
Pop–on captions work with two caption memories. One of
them is normally displayed while the other is being used to
accumulate new caption data. A new caption is popped–on
by swapping the two memories with the end of caption (EOC)
command. When the on–screen memory is erased, the
screen is blank (transparent) and the memory will default to
the row/column pointer at row 1, column 1 and monochrome
non–underlined.
When caption mode is selected, the decoder will process
any data following the resume caption loading (RCL) command (or the EOC). Normally, this command will be followed
by a preamble address code (PAC) to indicate the row, column, and character attributes to be used with the following
data. If no P AC is received the data will be added to the location last indicated by the row/column pointer prior to the receipt of the RCL command.
Paint–on caption mode is essentially equivalent to the
pop–on mode except that the data received after the resume
direct captioning (RDC) command is written to the on–screen
memory rather than the off–screen memory. All the rules for
P ACs, midcodes, etc., are otherwise the same.
Roll–up caption mode presents a “text” like display that is
limited to two, three, or four rows, depending on the resume
roll–up (RUn) command used. The PAC following the RUn
command is used as the BASE ROW for the ROLL–UP display. The BASE ROW will be the “bottom” row of the ROLL–
UP display. In this case black box does not appear until
characters are being displayed and box is only wide enough
to provide a leading and trailing box in each line. The new
data appears in the bottom row and as each carriage return
is received, the row scrolls up and the new data added to the
bottom. When the number of rows indicated by the resume
command has been reached, the data in the top row scrolls
off as new data is added to the bottom.
The TAB (INDENT) PAC permits placing captions starting
at four character boundaries in any caption row. The TAB
OFFSET command provides the means for adjusting the
starting position for a caption at any column position in the
current row.
XDS Mode Display
Two XDS display modes are provided. One provides information about the current program that would be of interest
for “channel grazing”. The second display shows the grazing
packets plus additional XDS packets which will inform the
viewer about the program content. Information will be displayed as it is received. The display uses the drop shadow
mode with 15 scan lines per row.
The XDSG mode is the GRAZE (channel grazing) display .
The display contains three rows of information at the top of
the screen, formatted for easy reading. They will contain the
following XDS packet information:
Row 1, Grn – Network Name – Call Letters
Row 2, Ital, Und – Program Name (title)
Row 3, Cyan – Program Length – Time In Show
The XDSF mode is the FULL (information) display. This
display shows the same information as the GRAZE display
and adds the program type as well the first four program description rows (if transmitted). Although XDS defines eight
program description rows, the first four are identified as containing the most important information and are the ones most
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